| With the depletion of fossil energy and the deterioration of ecological environment on the earth, renewable resources gradually become the research hot spot. Lignin is the second abundant renewable natural polymer and more and more interest has been paid on its utilization. Derived from plants and environmental friendly, lignosulfonate from sulfite pulping waste liquid is a kind of outstanding dye dispersant with good high temperature stability. However, the current lignosulfonate in our country comes from complex material and the effective component content is low and lack of modification. There are also some disadvantages when used as dye dispersant, relating to serious fiber staining, dye reduction and bad high temperature stability, so they are used as low-end products. Alkali lignin, the by-product acidificated from alkaline pulping black liquor, has the characteristics of high purity, abundant, low price and high chemical activity. Its chemical modification to prepare lignin dye dispersant of good performance has become a research hotspot in the field of lignin utilization.In this paper,the molecular structure and performance as dye dispersant of different lignosulfonates were studied. The results showed that lignosulfonate had better high temperature stability and staining property than sulfonated alkali lignin. Especially, poplar sodium lignosulfonates with high weight average molecular weight(Mw) had good high temperature stability. Bamboo sodium lignosulfonates with high Mw and low chromaticity and phenol hydroxyl content had light fiber staining. The results showed that higher molecular weight and sulfonic group content can serve more steric hindrance and electrostatic repulsion, giving lignosulfonates better high temperature stability. Darker color and high phenolic hydroxyl group content of lignosulfonates will cause more serious fiber staining, while higher sulfonic group content availed its reduction of staining on fiber.Sulfomethylated alkali lignin(SAL)with high sulfonic group content was prepared from pine alkali lignin(AL) through high temperature sulfomethylation. The appropriate modified conditions were that w(AL) was 25.0%, p H of solution was 11.0,n(Na2SO3)∶n(CH2O) was 3.5∶1, reaction temperature was 180℃,reaction time was 4 h. The IR spectra of purified optimizing product showed that the sulfonic group peak at 1039 cm-1 appeared in SAL prepared by sulfomethylation compared with AL, proving that sulfonic group was successfully introduced into lignin molecules. Disperse blue 79 was prepared with SAL, the performance results showed that SAL with the sulfonic group content of 1.2~1.4mmol·g-1 possessed good comprehensive performance, Higher sulfonic acid group content gave SAL better high temperature stability. The lowest average particle size of dye dispersant after 130℃ treatment was 14.35μm,which is far less than those of commercial dye dispersant UNA(86.13μm). SAL also possessed good grinding effect, and the particle size of dye dispersant after grinding was about 0.6μm,similar to UNA and Guotai. The higher sulfonic group content of SAL was, the lower its contamination rate on the fiber was. However, SAL stained fiber more seriously than commercial dye dispersant UNA and Guotai, which need be further improved.Carboxymethylated sodium lignosulfonate(CSAL) with high carboxyl group content was prepared from SAL through carboxymethylation. The appropriate modified conditions were that n(Na OH)∶n(Cl CH2COOH) was 1.7∶1, reaction temperature was 70℃,reaction time was 1.5 h. The IR spectra of purified optimizing product showed that the carboxyl group stretching vibration C=O at 1727 cm-1 appeared in CSAL prepared by carboxymethylation compared with SAL, and its 13C-NMR spectra showed that the C atom of –COOH at 170.8ppm and the C atoms of –CH2 of carboxymethyl groups at 69.5 ppm and 65.7 ppm appeared in CSAL, proving that carboxyl group was successfully introduced into lignin molecules. CSAL-L、CSAL-M and CSAL-H dye dispersant with carboxyl group content of 1.00~1.70 mmol·g-1 were prepared from SAL-L、SAL-M and SAL-H whose sulfonic group content were 0.55 mmol·g-1、0.90 mmol·g-1 and 1.32 mmol·g-1 respectively. Disperse blue 79 was prepared with CSAL, the performance results showed that carboxymethylation can improve the fiber staining of lignin. The biggest reduce rate was 61.80% and the lowest contamination rate was 7.02. CSAL possessed good grinding effect. The average particle size of dye in the dye dispersion with CSAL was about 1 μm. CSAL-H had good high temperature stability and the lowest particle size of dye after 130℃ treatment was 34.87μm. Meanwhile, CSAL-H had good dyeing property and its corresponding K/S of fiber after dyeing was high. The phenolic group content of lignin can be reduced by carboxymethylation, leading to lower dye reduction.The adsorption properties of SAL with different sulfonic group content and CSAL-H with different carboxyl group content on the surface of the fiber and dye were studied by QCM-D. The results showed that the increase of sulfonic group and carboxyl group content of lignin can enhanced electrostatic repulsion between it and negatively charged fiber and weaken hydrophobic effect and hydrogen bonding interaction, leading to lower adsorption amount of lignin on fiber and more loose adsorption layer. With the increase of sulfonic group and carboxyl group content of lignin, its adsorption amount on the surface of dye increased and then decreased, and the conformation and dense degree of adsorption layer had little difference. When p H = 5, ionization degree of carboxyl was low and its effect on adsorption properties of lignin on the surface of fiber and dye was less than that of sulfonic group.The study of sulfomethylation and carboxymethylation of lignin and its application as dye dispersant provided a technique route and basic data for the green and efficient utilization of lignin and the preparation of new lignin dye dispersant. CSAL-H product had significant modified fiber staining and good high temperature stability, grinding effect and dye reduction at the same time. This may replace the dwindling fossil energy, which has great practical significance on solve the energy shortage and environmental pollution and important significance on dyeing and printing, dyeing and lignin industry。... |
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